1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device and a fabrication method thereof.
2. Discussion of the Background Art
A light-emitting diode (LED) is a type of semiconductor device that converts electricity to infrared or visible light using properties of a compound semiconductor and is used as indicator lights in electronic home appliances, remote control devices, electronic display boards, indicators and automation apparatuses.
The operation principle of such an LED is based on energy level of a material. That is, electrons and holes in a material move through and rejoin at a p-n junction when electrically biased in the forward direction. As a result, light is emitted from the p-n junction as energy level of the material is lowered due to the electron-hole rejoin.
Generally, LEDs are manufactured in a very small size about 0.25 mm2 and packaged using a lead frame, a printed circuit board (PCB) and a epoxy molding compound. Recently, the most common package for LEDs is a 5 mm (T 1¾) plastic package, but new packages for LEDs are being developed depending on LEDs application fields. The color emitted by the LEDs depends on the wave length which is controlled by chemical composition of a semiconductor material used.
As components for information technology and telecommunications are getting smaller and slimmer, various kinds of parts thereof, such as resistor, condenser, noise filter and so on, also become much smaller. To keep up such trend, LEDs are manufactured in a surface mount device (SMD) type package so as to be mounted on a PCB directly.
Accordingly, LED lamps used as display devices are being packaged in the SMD type recently. Such SMD-type LEDs can substitute related art simple light lamps and be used as light display apparatus, character display apparatus and image display apparatus for emitting various colored light.
FIG. 1 is a cross-sectional view of an LED in accordance with a related art. With reference to FIG. 1, a method of manufacturing an LED will be described below.
Referring to FIG. 1, a sapphire substrate 10 composed of mainly Al2O3, is provided with a GaN buffer layer 1 made of gallium nitride (GaN) thereon. Then, an undoped GaN layer 3 is formed on the GaN buffer layer 1.
Generally, group three elements in the periodic table are grown on the sapphire substrate 10 by a Metal Organic Chemical Vapor Deposition (MOCVD) method at a growth pressure ranging from 200 to 650 torr to be a layer. That is, the GaN buffer layer 1 and the GaN layer 3 are formed by the MOCVD method.
Next, an n-type GaN layer 5 is formed on the undoped GaN layer 3 using silicon such as monosilane SiH4 or disilane Si2H6.
On the n-type GaN layer 5, an active layer 7 is formed. The active layer 7 serving as a light-emitting area is a semiconductor layer containing Indium Gallium Nitride (InGaN) as light-emitting material therein. After the active layer 7 is grown, a p-type GaN layer 9 is formed on the active layer 7. The p-type GaN layer 9 is formed using Mg-based group two elements in the periodic table.
The p-type GaN layer 9 is complementary layer to the n-type GaN layer 5 which supplies electrons to the active layer 7 when a voltage is applied thereto.
On the contrary, the p-type GaN layer 9 supplied holes to the active layer 7 when a voltage is applied so that the electrons and holes join in the active layer 7 and light is emitted from the active layer 7.
Even though not shown, a transparent metal layer (TM) made of a conductive material (not shown) is formed on the p-type GaN layer 9 to shed the light emitted from the active layer 7 outside.
A light-emitting device manufacturing process is completed as p-type electrode is formed, after the TM layer is formed.
However, the above light-emitting device in accordance with the related art is disadvantageous in that Mg—H complexes having an insulating property is formed on the p-type GaN layer as Mg reacts with atomic H generated from decomposition of NH3 gas when an Mg doping process is performed to form an electrical contact layer on the surface of the p-type GaN layer. The Mg—H complexes serve as an obstacle to the Mg doping, so that it becomes difficult to increase the number of hole carriers in the p-type GaN layer even though Mg is doped at high dose.
Such Mg—H complexes are caused as atomic H combines with Mg contained in trimethyl gallium (TMG) or double cycle pentadienyl magnesium (DCP Mg) organic substance used for crystal growth after the growth of the p-type GaN layer, or caused due to decomposition of NH3 gas which is needed to maintain the p-type GaN layer in NH3 ambient to prevent formation of nitrogen vacancy (N-vacancy) in the p-type GaN layer, wherein such N-vacancy is generated due to the nitrogen out-diffusion upon cooling the p-type GaN layer after its growth. That is, atomic hydrogen is generated when the NH3 gas is thermally decomposed and permeates into the GaN layer through treading dislocation holes existing on the surface of the GaN layer.